Create AccumulatingVelocityTrackerStrategy

This is a partial implementation of VelocityTrackerStrategy, that stores
data points during "add" operations. Extracting this logic into a common
class helps avoid duplicated logic across several strategies that do the
exact same thing when adding new movements. It also helps ease future
updates/optimizations.

Bug: 267211645
Test: atest libinput_tests
Change-Id: I116e978b070aa451813fefa384ccc65e10ea45a0

2 files changed, 36 insertions, 119 deletions

diff --git a/include/input/VelocityTracker.h b/include/input/VelocityTracker.h
index 5a23e8dca5..6d51515cb3 100644
--- a/include/input/VelocityTracker.h
+++ b/include/input/VelocityTracker.h
@@ -152,11 +152,34 @@ public:
     virtual std::optional<float> getVelocity(int32_t pointerId) const = 0;
 };
 
+/**
+ * A `VelocityTrackerStrategy` that accumulates added data points and processes the accumulated data
+ * points when getting velocity.
+ */
+class AccumulatingVelocityTrackerStrategy : public VelocityTrackerStrategy {
+public:
+    void addMovement(nsecs_t eventTime, int32_t pointerId, float position) override;
+    void clearPointer(int32_t pointerId) override;
+
+protected:
+    struct Movement {
+        nsecs_t eventTime;
+        float position;
+    };
+
+    // Number of samples to keep.
+    // If different strategies would like to maintain different history size, we can make this a
+    // protected const field.
+    static constexpr uint32_t HISTORY_SIZE = 20;
+
+    std::map<int32_t /*pointerId*/, size_t /*positionInArray*/> mIndex;
+    std::map<int32_t /*pointerId*/, std::array<Movement, HISTORY_SIZE>> mMovements;
+};
 
 /*
  * Velocity tracker algorithm based on least-squares linear regression.
  */
-class LeastSquaresVelocityTrackerStrategy : public VelocityTrackerStrategy {
+class LeastSquaresVelocityTrackerStrategy : public AccumulatingVelocityTrackerStrategy {
 public:
     enum class Weighting {
         // No weights applied.  All data points are equally reliable.
@@ -177,8 +200,6 @@ public:
     LeastSquaresVelocityTrackerStrategy(uint32_t degree, Weighting weighting = Weighting::NONE);
     ~LeastSquaresVelocityTrackerStrategy() override;
 
-    void clearPointer(int32_t pointerId) override;
-    void addMovement(nsecs_t eventTime, int32_t pointerId, float position) override;
     std::optional<float> getVelocity(int32_t pointerId) const override;
 
 private:
@@ -187,23 +208,12 @@ private:
     // changes in direction.
     static const nsecs_t HORIZON = 100 * 1000000; // 100 ms
 
-    // Number of samples to keep.
-    static const uint32_t HISTORY_SIZE = 20;
-
-    struct Movement {
-        nsecs_t eventTime;
-        float position;
-    };
-
     float chooseWeight(int32_t pointerId, uint32_t index) const;
 
     const uint32_t mDegree;
     const Weighting mWeighting;
-    std::map<int32_t /*pointerId*/, size_t /*positionInArray*/> mIndex;
-    std::map<int32_t /*pointerId*/, std::array<Movement, HISTORY_SIZE>> mMovements;
 };
 
-
 /*
  * Velocity tracker algorithm that uses an IIR filter.
  */
@@ -238,41 +248,26 @@ private:
 /*
  * Velocity tracker strategy used prior to ICS.
  */
-class LegacyVelocityTrackerStrategy : public VelocityTrackerStrategy {
+class LegacyVelocityTrackerStrategy : public AccumulatingVelocityTrackerStrategy {
 public:
     LegacyVelocityTrackerStrategy();
     ~LegacyVelocityTrackerStrategy() override;
 
-    void clearPointer(int32_t pointerId) override;
-    void addMovement(nsecs_t eventTime, int32_t pointerId, float position) override;
     std::optional<float> getVelocity(int32_t pointerId) const override;
 
 private:
     // Oldest sample to consider when calculating the velocity.
     static const nsecs_t HORIZON = 200 * 1000000; // 100 ms
 
-    // Number of samples to keep.
-    static const uint32_t HISTORY_SIZE = 20;
-
     // The minimum duration between samples when estimating velocity.
     static const nsecs_t MIN_DURATION = 10 * 1000000; // 10 ms
-
-    struct Movement {
-        nsecs_t eventTime;
-        float position;
-    };
-
-    std::map<int32_t /*pointerId*/, size_t /*positionInArray*/> mIndex;
-    std::map<int32_t /*pointerId*/, std::array<Movement, HISTORY_SIZE>> mMovements;
 };
 
-class ImpulseVelocityTrackerStrategy : public VelocityTrackerStrategy {
+class ImpulseVelocityTrackerStrategy : public AccumulatingVelocityTrackerStrategy {
 public:
     ImpulseVelocityTrackerStrategy(bool deltaValues);
     ~ImpulseVelocityTrackerStrategy() override;
 
-    void clearPointer(int32_t pointerId) override;
-    void addMovement(nsecs_t eventTime, int32_t pointerId, float position) override;
     std::optional<float> getVelocity(int32_t pointerId) const override;
 
 private:
@@ -281,21 +276,10 @@ private:
     // changes in direction.
     static constexpr nsecs_t HORIZON = 100 * 1000000; // 100 ms
 
-    // Number of samples to keep.
-    static constexpr size_t HISTORY_SIZE = 20;
-
-    struct Movement {
-        nsecs_t eventTime;
-        float position;
-    };
-
     // Whether or not the input movement values for the strategy come in the form of delta values.
     // If the input values are not deltas, the strategy needs to calculate deltas as part of its
     // velocity calculation.
     const bool mDeltaValues;
-
-    std::map<int32_t /*pointerId*/, size_t /*positionInArray*/> mIndex;
-    std::map<int32_t /*pointerId*/, std::array<Movement, HISTORY_SIZE>> mMovements;
 };
 
 } // namespace android
diff --git a/libs/input/VelocityTracker.cpp b/libs/input/VelocityTracker.cpp
index a88aa485fc..ac042c5790 100644
--- a/libs/input/VelocityTracker.cpp
+++ b/libs/input/VelocityTracker.cpp
@@ -370,21 +370,12 @@ VelocityTracker::ComputedVelocity VelocityTracker::getComputedVelocity(int32_t u
     return computedVelocity;
 }
 
-// --- LeastSquaresVelocityTrackerStrategy ---
-
-LeastSquaresVelocityTrackerStrategy::LeastSquaresVelocityTrackerStrategy(uint32_t degree,
-                                                                         Weighting weighting)
-      : mDegree(degree), mWeighting(weighting) {}
-
-LeastSquaresVelocityTrackerStrategy::~LeastSquaresVelocityTrackerStrategy() {
-}
-
-void LeastSquaresVelocityTrackerStrategy::clearPointer(int32_t pointerId) {
+void AccumulatingVelocityTrackerStrategy::clearPointer(int32_t pointerId) {
     mIndex.erase(pointerId);
     mMovements.erase(pointerId);
 }
 
-void LeastSquaresVelocityTrackerStrategy::addMovement(nsecs_t eventTime, int32_t pointerId,
+void AccumulatingVelocityTrackerStrategy::addMovement(nsecs_t eventTime, int32_t pointerId,
                                                       float position) {
     // If data for this pointer already exists, we have a valid entry at the position of
     // mIndex[pointerId] and mMovements[pointerId]. In that case, we need to advance the index
@@ -412,6 +403,14 @@ void LeastSquaresVelocityTrackerStrategy::addMovement(nsecs_t eventTime, int32_t
     movement.position = position;
 }
 
+// --- LeastSquaresVelocityTrackerStrategy ---
+
+LeastSquaresVelocityTrackerStrategy::LeastSquaresVelocityTrackerStrategy(uint32_t degree,
+                                                                         Weighting weighting)
+      : mDegree(degree), mWeighting(weighting) {}
+
+LeastSquaresVelocityTrackerStrategy::~LeastSquaresVelocityTrackerStrategy() {}
+
 /**
  * Solves a linear least squares problem to obtain a N degree polynomial that fits
  * the specified input data as nearly as possible.
@@ -834,39 +833,6 @@ LegacyVelocityTrackerStrategy::LegacyVelocityTrackerStrategy() {}
 LegacyVelocityTrackerStrategy::~LegacyVelocityTrackerStrategy() {
 }
 
-void LegacyVelocityTrackerStrategy::clearPointer(int32_t pointerId) {
-    mIndex.erase(pointerId);
-    mMovements.erase(pointerId);
-}
-
-void LegacyVelocityTrackerStrategy::addMovement(nsecs_t eventTime, int32_t pointerId,
-                                                float position) {
-    // If data for this pointer already exists, we have a valid entry at the position of
-    // mIndex[pointerId] and mMovements[pointerId]. In that case, we need to advance the index
-    // to the next position in the circular buffer and write the new Movement there. Otherwise,
-    // if this is a first movement for this pointer, we initialize the maps mIndex and mMovements
-    // for this pointer and write to the first position.
-    auto [movementIt, inserted] = mMovements.insert({pointerId, {}});
-    auto [indexIt, _] = mIndex.insert({pointerId, 0});
-    size_t& index = indexIt->second;
-    if (!inserted && movementIt->second[index].eventTime != eventTime) {
-        // When ACTION_POINTER_DOWN happens, we will first receive ACTION_MOVE with the coordinates
-        // of the existing pointers, and then ACTION_POINTER_DOWN with the coordinates that include
-        // the new pointer. If the eventtimes for both events are identical, just update the data
-        // for this time.
-        // We only compare against the last value, as it is likely that addMovement is called
-        // in chronological order as events occur.
-        index++;
-    }
-    if (index == HISTORY_SIZE) {
-        index = 0;
-    }
-
-    Movement& movement = movementIt->second[index];
-    movement.eventTime = eventTime;
-    movement.position = position;
-}
-
 std::optional<float> LegacyVelocityTrackerStrategy::getVelocity(int32_t pointerId) const {
     const auto movementIt = mMovements.find(pointerId);
     if (movementIt == mMovements.end()) {
@@ -939,39 +905,6 @@ ImpulseVelocityTrackerStrategy::ImpulseVelocityTrackerStrategy(bool deltaValues)
 ImpulseVelocityTrackerStrategy::~ImpulseVelocityTrackerStrategy() {
 }
 
-void ImpulseVelocityTrackerStrategy::clearPointer(int32_t pointerId) {
-    mIndex.erase(pointerId);
-    mMovements.erase(pointerId);
-}
-
-void ImpulseVelocityTrackerStrategy::addMovement(nsecs_t eventTime, int32_t pointerId,
-                                                 float position) {
-    // If data for this pointer already exists, we have a valid entry at the position of
-    // mIndex[pointerId] and mMovements[pointerId]. In that case, we need to advance the index
-    // to the next position in the circular buffer and write the new Movement there. Otherwise,
-    // if this is a first movement for this pointer, we initialize the maps mIndex and mMovements
-    // for this pointer and write to the first position.
-    auto [movementIt, inserted] = mMovements.insert({pointerId, {}});
-    auto [indexIt, _] = mIndex.insert({pointerId, 0});
-    size_t& index = indexIt->second;
-    if (!inserted && movementIt->second[index].eventTime != eventTime) {
-        // When ACTION_POINTER_DOWN happens, we will first receive ACTION_MOVE with the coordinates
-        // of the existing pointers, and then ACTION_POINTER_DOWN with the coordinates that include
-        // the new pointer. If the eventtimes for both events are identical, just update the data
-        // for this time.
-        // We only compare against the last value, as it is likely that addMovement is called
-        // in chronological order as events occur.
-        index++;
-    }
-    if (index == HISTORY_SIZE) {
-        index = 0;
-    }
-
-    Movement& movement = movementIt->second[index];
-    movement.eventTime = eventTime;
-    movement.position = position;
-}
-
 /**
  * Calculate the total impulse provided to the screen and the resulting velocity.
  *